TRANSMISSION ELECTRON-MICROSCOPY OBSERVATION OF CRYSTAL DEFECTS IN A NATURAL DIOPSIDE MINERAL

Transmission electron microscopy is used to carry out a number of observations on crystal defects and on alteration reactions in a natural porous diopside mineral. Dislocations as well as stacking faults and grain boundaries are observed. The observations confirm the Burgers and translation vectors found by other authors for diopside i. e. b equals left bracket 001 right bracket , and R parallel left bracket 100 right bracket . A Burgers vector b equals left bracket 101 right bracket , not mentioned in the literature is also determined here. Moreover a topotactic phase transformation is observed and analyzed in the same mineral. This phase is of the amphibole type. The amphibole phase resulted from the diopside phase following an alteration reaction indicating that diopside acted as an open chemical system free to exchange material with its surroundings. The amphibole phase grew on diopside in an orientation corresponding to the prevailing deformation twin orientation of diopside: K//1 equals (100), n//1 equals left bracket 001 right bracket .